At the present moment, a catalytic converter is used utilizing a honeycomb structural body as the catalyst support for purifying the exhaust gases exhausted from various kinds of engines and so on. The catalytic converter has a construction in which a catalyst coating layer 5 is supported on the surface of the partition walls 4 which divide and form a plurality of cells 3 of the honeycomb structural body, as shown in FIG. 10. The catalyst coating layer 5 consists mainly of oxides such as alumina, ceria, zirconia and so on, and precious metals such as platinum, rhodium, palladium and so on are supported in the ultra fine pores thereof as the catalyst active constituent. At the time of purifying the exhaust gases utilizing the catalytic converter 60 (honeycomb structural body 11), as shown in FIG. 8 and FIG. 9, it is performed that the exhaust gas is flowed into the cells 3 from the one end face 2a side, is contacted with the catalyst coating layer (not shown) on the surface of the partition walls 4, and then is flowed out to the outside from the other end face 2b side (refer to Japanese patent application laid-open 2003-33664, for example).
In case of purifying the exhaust gases utilizing these honeycomb structural bodies, it is necessary to improve the purifying efficiency by accelerating the transmission of the treating constituent contained in the exhaust gases as much as possible. In order to improve the purifying efficiency of the exhaust gases, it is necessary to decrease the hydraulic diameter of the cell, and increasing the surface area of the partition walls and so on. More concretely, the method, in which the number of cells per unit area (cell density) is increased, or the like is employed.
However, it is the fact that the sufficient catalyst performance is not obtained even by decreasing the hydraulic diameter by such increasing the cell density. In order to improve the catalyst performance much more, in these days, the study is performed to apply the plugged honeycomb structural body, in which one end of the cell is plugged and the other end of the adjacent cell is plugged alternately (to show a chequer pattern at the one end face of the honeycombs structural body) as used in the diesel particulate filter (DPF), to the catalyst support of the catalytic converter.
That is, in the honeycomb structural body in which plugging is applied to the cell, the exhaust gases flowed into from the one end face will flow out to the outside from the other end face after passing through the porous partition walls, therefore, it is possible to purify the exhaust gas by contacting the exhaust gas to the catalyst coating layer in the pores of the partition walls, if coating of the catalyst coating layer, which contains catalytic active constituent, is applied to the inner surface of the partition walls through which the exhaust gases pass. In the catalytic converter having this structure, the exhaust gas flows in the pores of the partition walls which having smaller hydraulic diameter compared with that of the cell, it is possible to make the distance between the exhaust gas and the catalyst coating layer to small, and also it is possible to increase the contact area between the exhaust gas and the catalyst coating layer, and as the result thereof, it is possible to expect the great improve of the catalyst performance.
However, for producing this kind of catalytic converter actually, coating the catalyst coating layer on the inner surface of the pores of the partition walls uniformly is very difficult, and there is a problem that sufficient catalyst performance is not shown, if the uniformity of the catalyst coating layer is damaged. Further, if trying to coat thinly the catalyst coating layer on the inner surface of the partition walls uniformly, the volume of the catalyst coating layer itself, that is, the absolute amount of the oxides constituting the catalyst coating layer is limited. Therefore, the distance between one precious metal particle and another precious metal particle supported in the catalyst coating layer or on the surface of the catalytic coating layer can not be sufficiently secured, the precious metal particle each other may start the cohesion at the time of actual use of the catalytic converter, and the catalytic activity may be lowered because of decreasing the total surface area of the precious metal particles. On the other hand, if trying to secure the absolute amount of the catalyst coating layer sufficiently, the pores of the partition walls are filled up with the catalyst coating layer, and therefore the passing resistance of the exhaust gas becomes too high.